1. Field of the Invention
The present invention relates to the treatment of sewage and other effluents to remove ammoniacal nitrogen (or NH.sub.4.sup.+ ion) therefrom in high concentrations
2. Description of the Prior Art
It is known to this art that ammoniacal nitrogen serves to promote the development of algae, and this can result in the eutrophication of rivers, streams and lakes, is toxic to aquatic fauna, accelerates the corrosion of pipes, especially those made from copper, and causes an increase in the chlorine demands and contact times required for proper sterilization of water which is to be rendered potable.
There exist a number of methods for removing ammoniacal nitrogen, the following being particularly representative:
(i) methods for the physicochemical treatment of sewage, such as oxidation/reduction of ammoniacal nitrogen, the removal of nitrogen compounds by precipitation, ion exchange or stripping;
(ii) biological treatments using nitrifying microorganisms responsible for aerobic nitrification of ammoniacal nitrogen.
By "nitrification" of NH.sub.4.sup.+ ions is intended the oxidation of the NH.sub.4.sup.+ ions to nitrite (NO.sub.2.sup.-) and/or nitrate (NO.sub.3.sup.2-) ions and, if desired, the oxidation of such nitrite ions to nitrate ions.
By "aerobic biological nitrification" are intended oxidation reactions such as described above, which occur in the presence of air and/or oxygen, using microorganisms (bacteria, etc.) that, in the presence of oxygen, serve to carry out said oxidation.
The "biomass" most typically employed is a mixture of nitriting bacteria (for example the Nitrosomonas) and of nitrating bacteria (for example Nitrobacters).
It is also possible to employ nitrifying bacteria, exemplary of which being Arthrobacter globiformis, Aspergillus flavus and Aspergillus ventii.
In the biological processes of aerobic nitrification, it is generally preferred to fix the microorganisms or biomass on a solid support in granular form; this makes it possible to attain higher biomass concentrations in the reactor and to prevent bacteria which are too light from being entrained out of the reactor.
The known supports are inert vis-a-vis the nitrifying activity of the biomass, namely, they do not take part in the nitrification.
Supports based on active charcoal, diatomaceous earths, sand, ceramics or glass beads are exemplary thereof.